The present invention relates to an acoustic positioning method and system and, more particularly, but not exclusively to a method and system for synchronization of transmissions between a positional element and a positioning device.
The application of positioning, or location awareness, is commonly divided according to the size of the space in which the positional element should be located.
The space size ranges from the personal area, which range is typically up to 1 meter, the room area which range is typically up to 10 meters, the local area, such as a warehouse, which range is up to 100 meters, and wide area which is typically an open space.
Some applications require positioning in three dimensions. Other applications, typically when the object is known to be located close enough to a known surface, such as the floor, require positioning in two dimensions only, and some applications require only the measurement of the distance between the positional element and the positioning device.
There are several methods for locating elements and most of them are based on measuring the time of arrival of a signal transmitted or reflected from the positional element.
There are numerous applications for small space positioning, that is, positioning within personal, room and local areas. The main applications involve pointing devices for computer interaction, and robotics and machine control, locating portable home appliances and especially toys, locating inventory in warehouses, hospital wards, etc.
1. Personal Area Positioning—Computer pointing devices, digital pens and touch screens
3-D Mouse:
A 3D mouse uses electromagnetic or ultrasonic positioning techniques to indicate its position in 3-D space to a monitoring device. The cordless mice in use today use Bluetooth and similar radio and IR transmitters for wireless connectivity. The radio or IR only takes care of the wireless connectivity, that is the signaling issue. Positioning generally involves a movement tracker in the mouse itself, which may be optically based. Simple movement tracking gives a 2D solution. 3D solutions can be produced, for example using either of the following:
Acoustic:
A mouse emits ultrasonic and IR pulses that are received by a desktop receiver. By measuring the time of flight, triangulation can be performed.
IR Sensors:
A mouse emits IR pulses whose angles are measured by a desktop receiver. Several angle sensors allow three-dimensional triangulation thus obtaining the special position.
PC Tablets and Styluses:
A PC tablet uses a digital pen or stylus. The stylus enables interactions including writing directly on a graphic tablet, PC tablet, PC screen, PDA screen, cellphone screen and on any other computer enabled surface, screen or tablet. Available solutions work with passive or active electromagnetic or acoustic technologies.
Digital Pens
Digital pens are pointing devices used for electronic detection of handwriting or hand drawing, or for general pointing. The digital pens generally use technologies such as acoustics, IR and light. Other versions use accelerometers that sense accelerations and transmit the data to a positioning assembly. Another version is a camera that analyzes small printing codes on special paper to determine its position. Other pens use electromagnetic (including passive & active), and other technologies for their operation. Some of the digital pens are an autonomous unit, meaning the pen works independently, providing its own fully processed co-ordinates as an output, and such is typical of optical and digital camera based units. Others, especially acoustic and electromagnetic devices, require a receiving or sensing unit. Digital Pens are widely used with PC's, laptops, PDAs, cellular telephones, electronic books, and the like.
Touch Screens:
Touch screens generally comprise sensors embedded within or near a computer screen in order to receive input from the screen. Some technologies include coating the screen with special material that can sense physical contact, the material featuring electrical resistance, electrical capacitance or a surface acoustic wave (SAW) material. Other technologies include embedding of sensors around the screen. The sensors may be IR, acoustic, SAW and others.
2. Room Area Positioning—Interactive Whiteboards and Toys
Interactive Whiteboards
The interactive whiteboard is a whiteboard that captures written data from the board into an associated computer. One of the common technologies in this field is acoustic positioning: a marker is placed in a sleeve that transmits beacon signals which are picked up and analyzed by a dedicated device also placed near the whiteboard. In some cases an IR or electromagnetic signal is transmitted along with the acoustic beacon for better accuracy and for simplicity. Another common technology is electromagnetic: the above mentioned marker sleeve transmits an electromagnetic field, which is picked up by special loops on the back of the whiteboard.
Technology using electrical resistance is also used. In such a case the surface of the whiteboard is coated with resistive material. Pressure is applied to the coating, and the pressure causes a local change in the resistive properties of the board. From the changes, the controller is able to obtain a x, y position from the applied pressure.
Technology using electrical capacitance, which is similar to the resistive, can also be used. Again, pressure is used, this time to change the capacitance properties of the board. Then, the controller is able to obtain the x, y position
Toys
It is relatively uncommon, due to the high cost, to have toys in which one unit can be aware of the location of a second unit.
In a very basic example, one toy notes that there is another toy nearby, prompting a reaction, for example talking. In a more sophisticated example, one toy knows more or less where the other toy is.
In the future it is hoped to provide a yet more sophisticated example in which one unit can successfully pass an object to the next one and vice versa. Further in the future a toy is envisaged, in which twenty-two soccer robots run around passing the ball one to another. The robots calculate where to kick according to the locations of the other robots on the same and opposite teams. To provide each of the twenty-two robots with the computing and control power in order to play a game of soccer produces a very expensive and complex solution.
Generally, toy technology has to be provided at low cost and current technology is relatively expensive. Specific technologies each have their drawbacks:
Infrared sensors—IR can be used to indicate presence in the vicinity of a second object. At a higher level it can show a general direction.
Accelerometers—the disadvantages of accelerometers are discussed above in the section on pointing devices.
Acoustic—Acoustic devices are relatively expensive. Only a single unit can be used in the same environment, energy use is relatively high, and the devices are difficult to miniaturize.
Local Area Positioning—Robotics and Machine Control
In recent years several new robotics products have reached the prototype stage and beyond. The robotics products include freely moving robots for different applications. The applications include lawn mowers, pool cleaners, spy and bomb disposal robots with cameras and remote control and many more. Such robots typically use their own sensing together with pre-programming to find their way around in their surrounding environment.
Possible new applications include an autonomous vacuum cleaner. One or more vacuum cleaners may roam automatically around the premises, vacuuming dirt and transferring the dirt to either fixed location units or roaming units. The unit that vacuums may autonomously locate the receiving unit to which it delivers the dirt and dock therewith in order to deliver the dirt.
Drawbacks
All the technologies mentioned above, except the acoustic, need sensors on the positioning plane: the electromagnetic solution needs antenna loops on the back of the board, the pen with the camera needs special digitized paper and the touch-screens need special coatings. The need for sensors adds both to the cost of the final product, and furthermore provides an unnatural restriction on use in that it does not allow the user to use arbitrary planes, such as a cluttered desk surface, as a working platform.
Some of the technologies are limited to two-dimensional locations. But even those that can manage a third dimension do not currently provide accurate information of the third dimension. For example a stylus based on electromagnetic detection can be detected when hovering above a screen, but it is not possible to tell accurately how high it is. The detector simply determines that it is present.
There are other drawbacks specific to certain of the technologies. For instance, IR positioning has difficulties working with direct sun. Existing acoustic solutions have serious limitations in acoustically noisy environments, in particular in the all-important industrial environment, where ultrasound noise is most common.
Solutions that use wireless protocols as Bluetooth may suffer from protocol collisions, and from interference with other wireless equipment, such as WLAN equipment.
All the technologies that are based on measuring the time of flight of a signal transmitted by the positional element and received by the positioning device require accurate synchronization between the transmitter and the receiver to compensate for their clocks inaccuracy and drift.
Acoustic positioning methods and devices are known in the art, including, but not limited to, the following US patents: U.S. Pat. Nos. 6,876,356; 6,875,933; 6,841,742; 6,822,641; 6,731,270; 6,724,371; 6,717,073; 6,654,008; 6,633,280; 6,628,270; 6,556,694; 6,539,363; 6,535,206; 6,529,189; 6,517,266; 6,501,461; 6,456,567; 6,456,280; 6,424,340; 6,414,673; 6,404,416; 6,373,003; 6,335,723; 6,326,565; 6,313,825; 6,310,615; 6,300,580; 6,292,180; 6,292,177; 6,266,051; 6,265,676; 6,229,526; 6,211,863; 6,195,446; 6,191,778; 6,177,927; 6,153,836; 6,147,681; 6,144,367; 6,124,847; 6,111,565; 6,108,271; 6,104,387; 6,100,877; 6,067,080; 5,977,958; 5,907,130; 5,883,338; 5,872,743; 5,866,856; 5,818,421; 5,798,755; 5,793,361; 5,768,616; 5,750,941; 5,717,168; 5,657,054; 5,657,053; 5,635,951; 5,581,269; 5,557,301; 5,548,092; 5,539,159; 5,525,764; 5,517,579; 5,515,051; 5,500,492; 5,478,976; 5,308,936; 5,144,594; 5,128,660; 5,111,005; 5,054,005; 5,007,085; 4,991,148; 4,965,635; 4,814,552.
The reader is also referred to applicants prior application No. IL03/00309 filed Apr. 14, 2003, the contents of which are hereby incorporated by reference.
All the problems discussed above are further enhanced in the multi user environment, where one or more positioning devices have to locate several positional elements, and even more so, when the positional elements may roam between positioning devices.
There is thus a widely recognized need for, and it would be highly advantageous to have an infrared communications system and method devoid of the above limitations.